It has been estimated that 55% of stroke survivors have a nonfunctional (paralyzed) upper extremity following their stroke. A further 30% have partial use of their upper extremities, with limited range of motion and strength. Most victims of stroke are unable to perform their activities of daily living in the same manner as before the stroke, due to these limitations on motion and strength. Accordingly, one of the most common symptoms in a stroke survivor is mild to severe paresis of an upper extremity.
Likewise, one of the more common effects of spinal cord injury is nonfunctional or limited function to the upper extremities. It has been estimated that 50% of the spinal cord injured individuals have some level of upper extremity impairment.
Treatment options, especially for those with severe paralysis of the upper extremity, are extremely limited. Constraint-induced movement therapy has been shown to be effective in recovering upper limb function, but only for mild paresis, for example, where patients are able to independently extend the fingers and wrist to some extent. Other new therapies are being explored, including robot-assisted therapy, biofeedback therapy, and virtual reality training. However, to date, these therapies have shown promise for individuals with mild paresis only.
Functional electrical stimulation (FES) therapy has been tested as interventions for acute and chronic stroke. For example, the NESS Handmasterm™ (also know as Bioness™ H200 system) is a multichannel neuroprosthesis, worn by the patient. Training with the device led to gains in small randomized trials, as an intervention for grasping impairment in both chronic hemiparesis and subacute hemiparesis due to stroke. In these studies, the device was used for 12 weeks, and positive results were seen as an increase in volitional hand tests for the FES group in contrast to a control group that performed task-oriented training without FES. Other studies have implemented FES therapy, and have demonstrated modest improvements in terms of upper extremity function and spasticity following 6 weeks and 18 weeks of use, both in home-based programs, and in clinical settings under the supervision of a trained FES practitioner.
Several stimulation systems in addition to the NESS Handmaster are known; most use several surface electrodes, a multi-channel stimulator and a pre-programmed sequence of stimulation that can be triggered by a switch, several switches, or signals from a sensor. Other stimulation systems use implantable electrodes, or fully implantable systems that use a pre-programmed stimulation that is controlled by a switch or sensory signal in an open- or closed-loop control scheme.
Most of the prior art stimulation systems comprise stimulation of more than one muscle group in patients with mild paresis. One of the more complex prior art systems is described in US 2004/0147975 A1 (incorporated herein by reference in its entirety) which describes electrical stimulation of neural pathways using a stimulation pattern that mimics natural flow of neural activities to the impaired upper extremity; generating the missing components of a functional movement in parallel with the voluntary exercising of the same functional movement based on the said patterned stimulation of the efferent neural pathways time-synchronized with volitional movement; and enhancing the afferent input by the said patterned electrical stimulation in time synchrony with the biological afferent activity caused by the functional movement of the limb. The published application teaches that therapy for motor relearning in persons with paresis caused by stroke should support a process of relearning optimally by functionally assisting the user to perform intended activities, which they may only be able to perform poorly or not without assistance. It is taught that the sensory feedback associated with the process of the activities assists with the relearning process of the brain. The publication teaches that the patterned stimulation of the muscles is synchronized with volitional movement or volition of movement (whether or not the patient is capable of any relevant movement without the stimulation); the electrical signals are perceived by the patient, which provides an enhanced afferent input in synchrony with biological afferent activity, i.e. exteroceptive signals as well as proprioceptive signals. The publication also teaches a control algorithm that causes the stimulator to provide stimulation patterns of muscle-inducing electrical signals which mimic the timing and modulation of muscles typically active in able-bodied humans, with signals including non-simultaneous peaks of activation of agonist and antagonist muscles during a single direction of movement, and appropriate coactivation of agonist and antagonist muscles needed for a desired functional movement. The patent teaches stimulation of finger flexors, finger extensors, thumb extension/adduction, and thumb opposition/flexion. Optionally, forearm flexion and extension, as well as forearm supination and pronation are stimulated.
It would be advantageous to provide a stimulation system that provides improved re-training and improved mobility and strength in patients with both mild and severe paralysis of upper extremities, caused by stroke or spinal cord injury.